Folkman and Kalluri suggest that most tumors don’t develop a blood supply that allows them to grow and progress to cancer, because people produce natural inhibitors of blood vessel growth, or angiogenesis. They write that a better understanding of these inhibitors may yield a new generation of nontoxic anticancer drugs that could be given preventively to people at high risk for developing the disease.
The essay cites autopsy studies revealing that more than a third of women aged 40 to 50 have small breast carcinomas, whereas only 1 percent are diagnosed with clinical breast cancer. Analagous findings hold for prostate cancer in men. Similarly, autopsies show that virtually all people aged 50 to 70 have small thyroid tumors, yet well below 1 percent are diagnosed with clinical thyroid cancer.
Folkman and Kalluri describe two phases of cancer, the first of which isn’t inherently lethal and where genetic mutations develop that transform normal cells in the body into cancerous cells. The second phase involves the dominance of growth factors secreted by a tumor to attract a blood supply over the defense provided by natural angiogenesis inhibitors.
A major current focus of Folkman’s Vascular Biology Program at Children’s Hospital Boston is on predicting the ‘angiogenic switch’ and delaying or preventing it with natural angiogenesis inhibitors. Preventive therapy could be offered to people with a genetically increased risk for cancer, people with a family history of cancer, and people whose cancer has been treated but may recur.